A. Field of the Invention
This invention relates to control systems, especially to call button systems for electrical elevator installations and to replacement units used in such systems.
B. Prior Art
For many years, capacitive call button systems have been used in connection with control systems for elevators. Those systems were actuated by the mere contact of the finger on a stationary button area which was capacitively coupled to a tube ignited by such touching. Recently, vandalism and crime have burgeoned and call button systems of this type have often been destroyed or mutilated by the vandals. Vandal-resistant push buttons are devices which have few edges that can be pried open or mutilated and which have condition lights effectively shielded from physical harm. In many cases, these new vandal-resistant push buttons have been substituted for the capacitive type call buttons presently in use. However, the mere substitution of these vandal-resistant push buttons would require expensive changes in the associated circuitry.
In order to avoid such changes, the present invention is designed to be easily substituted in conventional installations for the circuits between the vandal-resistant push buttons and the rest of the overall elevator control circuits thereby minimizing installation costs. One such replacement module, especially for a double riser call button system such as used on the floor of a building with two sets of push buttons on opposite sides of the hall, has been described in our copending application Ser. No. 735,953, filed Oct. 27, l976 and entitled "Elevator System Replacement Module." The present invention is intended to provide an improved substitute for capacitive type call button systems having considerably less heat sensitivity than such systems. It is also intended to provide an even more stable circuit than the one described in our copending application and has even more immunity to being triggered by stray noise in the electrical environment.